Coil spring unit, driving force transmitting device and image forming apparatus

ABSTRACT

A coil spring unit includes a coil spring; and a metal plate supporting the coil spring, the metal plate including a plurality of supporting portions cooperative with each other to support the coil spring, wherein the supporting portions are provided by bending the metal plate at bending lines and have supporting surfaces substantially perpendicular to the bending lines, respectively, and wherein the supporting surfaces are substantially parallel with outside tangential lines of the coil spring and support the coil spring.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a coil spring unit, a mechanical forcetransmitting device, and an image forming apparatus.

A coil spring has been in use in apparatuses in various fields.Referring to FIG. 10, there is disclosed in Japanese Utility PatentApplication No. H06-69446, an apparatus structured so that a coil spring102 is supported by a metallic member 103 having a pair of mutuallyopposing coil spring retaining portions. More specifically, the coilspring 102 is held to the metallic plate 103 by being sandwiched betweenthe mutually opposing surfaces 101 a of the pair of coil springretaining portions, by its peripheral portion 102 a.

This structural arrangement does not require additional components tokeep the coil spring 102 held to the metallic plate 103. Thus, thestructural arrangement disclosed in Japanese Utility Patent ApplicationsNo. H06-69446 is effective to reduce in cost an apparatus which employsa coil spring.

In the case of the structural arrangement disclosed in Japanese UtilityPatent Application No. H06-69446, however, the efficiency with which thecoil spring 102 can be inserted between the mutually opposing surfaces101 a in such a manner that the peripheral portion 102 a of the coilspring 102 comes into contact with the surfaces 101 a, was not takeninto consideration. The coil spring retaining portions 101, shown inFIG. 10, are formed by putting a piece of metallic plate 103 through acombination of a process of punching and a process of bending. Thebending process is affected not only by the error in the measurement ofa metallic mold used for punching process, but also, by the errors inthe bending process, which is attributable to the thickness and hardnessof the metallic plate 103. Thus, the process of bending the portions ofthe metallic plate 103, which are the precursors of the coil springretaining portions, tend to be low in accuracy. In other words, it israther difficult to yield a pair of coil spring retaining portions,which is highly accurate in the distance between the mutually opposingtwo surfaces 101 a.

Thus, it is customary to set the distance between the mutually facingtwo surfaces 101 a to be larger than the external diameter of the coilspring 102. With the distance between the two surfaces 101 a being setlarger than the external diameter of the coil spring 102, it does notoccur that the contact between the coil spring 102 and the surfaces 101a interferes with the insertion of the coil spring 102 between the twosurfaces 101 a. That is, the coil spring 101 can be easily insertedbetween the two surfaces 101 a. This setup, however, has its ownproblem. That is, if the metallic plate 103 is vertically positioned asshown in FIG. 10 when the coil spring 102 is attached to the metallicplate 103, the coil spring 102 tends to slip out of the space betweenthe two surfaces 101 a, and fall.

SUMMARY OF THE INVENTION

The present invention is for solving the problem described above. Thus,the primary object of the present invention is to provide a coil springunit which is superior to any conventional coil spring unit, in theefficiency with which a coil spring unit can be assembled.

According to an aspect of the present invention, there is provided acoil spring unit includes a coil spring; and a metal plate supportingsaid coil spring, said metal plate including a plurality of supportingportions cooperative with each other to support said coil spring,wherein said supporting portions are provided by bending said metalplate at bending lines and have supporting surfaces substantiallyperpendicular to the bending lines, respectively, and wherein saidsupporting surfaces are substantially parallel with outside tangentiallines of said coil spring and support said coil spring.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a typical image forming apparatus which iscompatible with the present invention; it shows the general structure ofthe apparatus.

FIG. 2 is a perspective view of a mechanical force transmitting deviceequipped with a coil spring unit.

FIG. 3 is a side view of the mechanical force transmitting deviceequipped with a coil spring unit, shown in FIG. 2.

FIG. 4 is an exploded perspective view of the coil spring unit; it showsthe process of assembling the unit.

FIG. 5 is a combination of perspective and front views of the assembledcoil spring unit.

Part (a) of FIG. 6 is a schematic drawing of a modified version of thecoil spring unit in the first embodiment, and part (b) of FIG. 6 is aschematic drawings of another modified version of the coil spring unitin the first embodiment.

FIG. 7 is a schematic drawing of another modified version of the coilspring unit in the first embodiment.

FIG. 8 is an exploded perspective view of the modified version of coilspring unit shown in FIG. 7; it is for showing how the unit isassembled.

FIG. 9 is a combination of side and front views of the assembled coilspring unit in the second embodiment of the present invention.

FIG. 10 is an exploded perspective view of a comparative (conventional)coil spring unit.

DESCRIPTION OF THE EMBODIMENTS Embodiment 1

Hereafter, referring to FIGS. 1-7, the coil spring unit, mechanicalforce transmitting device, and image forming apparatus in the firstembodiment of the present invention are described about their structure.

<Image Forming Apparatus>

FIG. 1 is a sectional view of the image forming apparatus 110, which isfor showing the structure of the image forming apparatus 110. The imageforming apparatus 110 shown in FIG. 1 has a photosensitive drum 18,which is an image bearing member. The photosensitive drum 18 isrotationally driven by a motor 7 shown in FIG. 7, in the clockwisedirection of FIG. 1.

While the photosensitive drum 18 is rotated in the clockwise directionof FIG. 1, the photosensitive drum 18 is uniformly charged by a chargeroller 19. The uniformly charged peripheral surface of thephotosensitive drum 18 is scanned by a beam 26 a of laser lightprojected from a laser scanner 26 while being modulated according to theinformation of the image to be formed. Consequently, an electrostaticlatent image, which reflects the information of the image to be formed,is effected on the peripheral surface of the photosensitive drum 18.

To the electrostatic latent image formed on the peripheral surface ofthe photosensitive drum 18, toner (developer) is supplied by adevelopment roller 27 a, with which a developing apparatus 27 isprovided. Thus, the electrostatic latent image is developed into a tonerimage. The developing apparatus 27 is provided with an unshown stirringmember for stirring the developer, the aforementioned development roller27 a, and an unshown supply roller which is for supplying thedevelopment roller 27 a with the developer in the developer container.These rollers also are rotationally driven by a motor 7 shown in FIG. 2.

Meanwhile, the sheets P of recording medium stored in a sheet feedercassette 104 are moved one by one out of the cassette 104, and into themain assembly of the image forming apparatus 110, by the coordination ofa feed roller 105 and a separation roller 20. Then, each sheet P ofrecording medium is conveyed further by a pair of conveyance rollers106, while remaining pinched by the pair of conveyance rollers 106,until it comes into contact with the nip of a pair of registrationrollers 21, which are remaining stationary. As the sheet P is pressedfrontward with respect to the sheet conveyance direction, with itsleading edge remaining in contact with the nip, it is corrected inattitude by its resiliency, if it was conveyed askew.

Thereafter, the sheet P of recording medium is conveyed to the transfernip N1 formed between the photosensitive drum 18 and a transfer roller19, by the pair of registration rollers 19, while remaining pinched bythe pair of registration rollers 19, in synchronism with the timing withwhich the toner image formed on the peripheral surface of thephotosensitive drum 18 arrives at the transfer nip N1.

As transfer bias is applied to a transfer roller 107 from an unshowntransfer bias power source, the toner image formed on the peripheralsurface of the peripheral surface of the photosensitive drum 18 (imagebearing member) is transferred onto the sheet P of recording medium. Thetransfer roller 107 is rotationally driven by the motor 7 shown in FIG.2. Transfer residual toner, that is, the toner remaining on theperipheral surface of the photosensitive drum 18 after the transfer, isscraped away by an unshown cleaning blade, and then, is recovered into acleaner 25.

After the transfer of an unfixed toner image onto the sheet P ofrecording medium in the transfer nip N1, the sheet P is conveyed to afixing apparatus 108 by the combination of the photosensitive drum 18and transfer roller 107 while remaining pinched by the combination, andthen, is conveyed through the fixing apparatus 108 while remainingpinched between the fixation roller 108 a and pressure roller 108 b ofthe fixing apparatus 108. While the sheet P is conveyed through thefixing apparatus 108, the unfixed toner image on the sheet P isthermally fixed to the sheet P; it is melted by the fixation roller 108a, and becomes fixed to the sheet P as it cools down. The fixationroller 108 a and pressure roller 108 b also are rotationally driven bythe motor 7 shown in FIG. 2.

After being conveyed by the combination of the fixation roller 108 a andpressure roller 108 b while remaining pinched by the two rollers 108 aand 108 b, the sheet P is conveyed further by a pair of dischargerollers 109 while remaining pinched by the discharge rollers 109, andthen, is discharged onto a delivery tray 22 by the discharge rollers109. The discharge rollers 109 also are rotationally driven by the motor7 shown in FIG. 2.

The feed roller 105, conveyance rollers 106, registration rollers 21,transfer roller 107, photosensitive drum 18, fixation roller 108 a,pressure roller 108 b, discharge rollers 109, which are shown in FIG. 1,function as rotational members for conveying a sheet P of recordingmedium.

These rotational members also rotate by receiving rotational drivingforce (mechanical force) from the motor 7.

<Driving Force Transmitting Device>

Next, referring to FIGS. 2 and 3, a driving force transmitting device 1having the coil spring unit CS in this embodiment is described about itsstructure. FIG. 2 is a perspective view of the driving forcetransmitting device 1. FIG. 3 is a side view of the driving forcetransmitting device 1, as seen from the direction indicated by an arrowmark A in FIG. 2. It also shows the structure of the apparatus 1. By theway, for convenience sake, some parts of the driving force transmittingdevice 1 are not shown in FIG. 3.

Referring to FIGS. 2 and 3, the image forming apparatus 110 isstructured so that its side plate 3 is utilized as a part of the drivingforce transmitting device 1. The driving force transmitting device 1shown in FIGS. 2 and 3 has the first side plate 3 (metallic plate), themotor 7 attached to the side plate 3, a driving force transmittingportion 8, and the second side plate 6. This side plate 3 (coil springholding member) is provided with a spring retaining portion 14.

The coil spring unit CS has: a coil spring 2 (compression spring); andthe first side plate 3, as a supporting member, to which the coil spring2 is attached in such a manner that one (2 c) of the lengthwise endsurfaces of the coil spring 2 in terms of the direction which isparallel to the axial line of the coil spring 2 remains in contact witha the first side plate 3. Further, the driving force transmitting device1 has a gear assembly (gear train) unit AU which is in contact with theother end surface 2 d of the coil spring 2 with respect to the directionparallel to the axial line of the coil spring 2, that is, the oppositeend surface of the coil spring 2 from the end surface 2 c which is incontact with the first side plate 3 (supporting member). The coil spring2 is held by the combination of the first side plate 3 (supportingmember) and transmission gear assembly unit AU, by being sandwiched bythe combination.

<Transmission Gear Assembly Unit AU>

The transmission gear assembly unit AU has: a driver gear which rotatesby receiving rotational driving force from the motor 7 (driving forcesource); a follower gear 5 which is rotated by the driver gear 4; thesecond side plate 6 which has a pair of shafts by which the driving gear4 and follower gear 5 are rotatably supported, one for one. In thisembodiment, the driver gear 4 which rotationally slides on the other endsurface 2 d of the coil spring 2, and the follower gear 5, are inconnection to each other through a one-way clutch which comprises aratchet portion 4 a, with which the driver gear 4 is provided, and aratchet portion 5 a, with which the follower gear 5 is provided.

The driver gear 4 and follower gear 5 are rotatably supported by a shaft6 a with which the second side plate 6 is provided. The coil spring 2 isheld to the first side plate 3 so that its axial line coincides with theaxial line of the shaft 6 a. The follower gear 5 is supported by theshaft 6 a so that it is allowed to rotationally slide on a follow gearseat 6 a 1 with which the second side plate 6 is provided. To the drivergear 4, rotational driving force is transmitted from the drive shaft 7 aof the motor 7 (driving force source) by way of an idler gear 16. As therotational driving force is transmitted to the driver gear 4, it istransmitted to the follower gear 5 by way of the ratchet portions 4 aand 5 a, rotating thereby the follower gear 5. As the rotational drivingforce is transmitted to the follower gear 5, it is transmitted to theaforementioned various rotational members of the image forming apparatus110 by way of a gear 17.

Referring to FIG. 3, the coil spring 2, driver gear 4, and follower gear5 are held sandwiched between the first side plate 3 and second sideplate 6. Further, the shaft 6 a, with which the second side plate 6 isprovided, is put though a central through hole, with which the followergear 5 is provided, a central through hole, with which the driver gear 4is provided, and a through hole 3 a, with which the first side plate 3is provided. Then, it is locked to the first side plate 3 with a lockingmember 15 such as an E ring. Thus, the driver gear 4 and follower gear 5are supported by the shaft 6 a in such a manner that they are rotatableabout the shaft 6 a.

<Operation of Driving Force Transmitting Device>

Next, referring to FIGS. 2 and 3, the driving force transmitting device1 is described about its operation. The drive shaft 7 a of the motor 7,shown in FIG. 2, which is a source of the driving force, rotates inresponse to the signal which it receives from the unshown controller ofthe driving force transmitting device 1. As the drive shaft 7 a of themotor 7 rotates, the idler gear 16 is rotated by the rotation of thedrive shaft 7 a. Consequently, the driver gear 4, which is in mesh withthe idler gear 16, rotates.

Referring to FIG. 3, therefore, the follower gear 5 is rotated by therotation of the driver gear 4 by way of the ratchet portion 4 a of thedriver gear 4, and the ratchet portion 5 a of the follower gear 5, whichis in mesh with the ratchet portion 4 a of the driver gear 4. Inaddition, the gear 17, which is in mesh with the follower gear 5,rotates. This is how the driving force transmitting portion 8 isrotationally driven. Further, the various rotational members of theimage forming apparatus 110 are rotated by the driving force transmittedthereto by way of the gear train, which is in mesh with the gear 17 ofthe driving force transmitting portion 8. Since the rotational drivingforce is transmitted to the rotational members of the aforementionedconveying means, the sheet P of recording medium can be conveyed.

Next, referring to FIGS. 2 and 3, the operation of the driver gear 4 andthat of the follower gear 5 are described. As the rotational drivingforce of the motor 7 is transmitted to the driver gear 4 by way of theidler gear 16, the driver gear 4 rotates in the direction indicted by anarrow mark B in FIG. 2. The driver gear 4 always remains pressed towardthe follower gear 5 (rightward in FIG. 3) by the resiliency of the coilspring 2. Thus, as the driver gear 4 rotates in the direction indicatedby the arrow mark B, the ratchet portion 4 a of the driver gear 4 andthe ratchet portion 5 a of the follower gear 5 mesh with each other, andtherefore, the follower gear 5 rotates with the driver gear 4 in thedirection indicated by the arrow mark B in FIG. 3.

The fixation roller 108 a and pressure roller 108 b of the fixingapparatus 108 are rotated by the driving force transmitted theretothrough the gear 17, which is in mesh with the follower gear 5, and anunshown gear train. The fixing apparatus 108 thermally fixes the unfixedtoner image transferred onto the sheet P of recording medium, to thesheet P by applying heat and pressure to the sheet P and the unfixedtoner image thereon; the unfixed toner image is melted by the heatapplied thereto, and becomes fixed to the sheet P as it cools down. If asheet conveyance passage 23 is jammed by a sheet P of recording mediumwhile the sheet P is being conveyed through the fixation nip N2 betweenthe fixation roller 108 a and pressure roller 108 b, while remainingpinched between the two rollers 108 a and 108 b, a user is to stop themotor 7 of the image forming apparatus 110, and then, remove the sheetP.

As a user pulls the sheet P of recording medium, which is remainingpinched in the fixation nip N2 between the fixation roller 108 a andpressure roller 108 b, the fixation roller 108 a and pressure roller 108b are rotated by the sheet P because of the presence of the frictionbetween the sheet P and fixation roller 108 a, and the friction betweenthe sheet P and pressure roller 108 b.

Thus, the follower gear 5 is rotated in the direction indicated by thearrow mark B in FIG. 3, by the rotation of the fixation roller 108 a andthat of the pressure roller 108 b, which are transmitted to the followergear 5 by way of an unshown gear train, and the gear 17. However, thedriver gear 4 remains stationary, because the motor 7 of the drivingforce transmitting device 1 is not rotating. If the follower gear 5rotates in the direction indicated by the arrow mark B in FIG. 3 whilethe driving force transmitting device 1 is in the above-described state,the slanted surface of each of the protrusive portions (tooth portions)of the ratchet portion 5 a of the follower gear 5 presses on the slantedsurface of the corresponding protrusive portion of the ratchet portion 4a of the driver gear 4. Consequently, the driver gear 4 moves leftwardagainst the resiliency of the coil spring 2. Thus, the amount of forcewhich the user has to exert to dislodge the sheet which is remainingpinched by the fixation roller 108 a and pressure roller 108 b, from thefixation nip N2 in order to remove the jammed sheet from the imageforming apparatus 110, is relatively small.

<Spring Holding Portion>

Next, referring to FIGS. 4 and 5, the spring holding portion 14, withwhich the first side plate 3 is provided is described about itsstructure. FIG. 4 is a perspective view of the spring holding portion 14and coil spring 2 prior to the attachment of the coil spring 2 to thespring holding portion 14. Part (a) of FIG. 5 is a perspective view ofthe spring holding portion 14 and coil spring 2 after the attachment ofthe coil spring 2 to the spring holding portion 14. It shows thestructure of the assembled combination of the coil spring 2 and springholding portion 14. Part (b) of FIG. 5 is a side view of the assembledcombination 10 of the spring holding portion 14 and coil spring 2, asseen from the direction indicated by an arrow mark C in FIG. 4 and part(a) of FIG. 5.

The first side plate 3 shown in FIG. 4 has four (multiple) springretaining portions 9, which are integral parts of the first side plate3. The spring retaining portions 9 are formed by subjecting the firstside plate 3 to a punching process and a bending process. They protrudeinward of the spring holding portion 14 perpendicular to the surface 3 bof the first side plate 3. It is by these spring retaining portions 9that the coil spring 2 is held to the first side plate 3.

The top and bottom spring retaining portions 9(H1), which are invertical alignment with each other as shown in FIG. 4, are the same inthe direction in which they are bent relative to the first side plate 3,with respect to the circumferential direction of the through hole 3 awith which the first side plate 3 is provided. The left and right springretaining portions 9(H2), which are in horizontal alignment with eachother as shown in FIG. 4, are the same in the direction in which theyare bent relative to the first side plate 3, with respect to thecircumferential direction of the through hole 3 a with which the firstside plate 3 is provided. Further, the four spring retaining portions 9(pair of spring retaining portions 9(H1) and pair of spring retainingportions 9(H2)) are positioned 90 degrees apart with respect to thecircumferential direction of the hole 3 a. It is through the hole 3 a ofthe first side plate 3 that the tip portion of the shaft 6 a is put.

Each spring retaining portion 9 has a lateral surface 9 a, as a springretaining surface, which occurs during the aforementioned punchingprocess. The lateral surface 9 a is roughly perpendicular to the line 2of bending, that is, the line along which the spring retaining portion 9was bent relative to the main portion of the first side plate 3 duringthe aforementioned bending process. Referring to parts (a) and (b)Figure, it is by this lateral surface 9 a (retaining surface) that thecoil spring 2 is held to the first side plate 3 by its peripheralportion 2 a. Instead, the first side plate 3 may be structured so thatthe coil spring 2 is supported by its inward side 2 e, by the lateralsurface 9 a (retaining surface) as shown in part (a) of FIG. 6. Asdescribed above, the lateral surface 9 a (retaining surface) is asurface for retaining the coil spring 2, and is roughly perpendicular tothe line 2 along which the precursor of the spring retaining portion 9is bent during the bending process.

The first side plate 3 is structured so that the pair of springretaining portions 9 having the lateral surface 9 a are separated by180° from each other with respect to the circumferential direction ofthe hole 3 a, and also, that the two lateral surfaces 9 a oppose eachother. The distance L between the lateral surface 9 a of one of the pairof retaining portions 9(H1), and the lateral surface 9 a of the other ofthe pair of retaining portions 9(H1), is roughly the same as thediameter D1 of the peripheral portion 2 a of the coil spring 2. Thus,the coil spring 2 can snugly fit between the lateral surface 9 a of oneof the pair of coil retaining portions 9(H1), and that of the other ofthe pair of coil retaining portions 9(H1), in such a manner that theperipheral portion 2 a of the coil spring 2 remains in contact with thelateral surfaces 9 a in practical terms.

The distance L2 between the lateral surface 9 a of one of the pair ofretaining portions 9(H2), and the lateral surface 9 a of the other ofthe pair of retaining portions 9(H2), is set to be roughly 1 mm greaterthan the distance L1 (L2>L1). Although the coil spring 2 is held to thefirst side plate 3 in such a manner that it is sandwiched between thelateral surface 9 a of one of the pair of retaining portions 9(H1) andthat of the other of the pair of retaining portions 9(H1), if the coilspring 2 is displaced in such a horizontal direction that is parallel tothe surface 3 a of the first side plate 3, it comes into contact withthe lateral surface 9 a of one of the pair of retaining portions 9(H2)(retained by lateral surface 9 a).

Referring to FIG. 4, each coil spring retaining portion 9 has a topsurface 9 e (end surface in terms of left-right direction in FIG. 3) anda lateral surface 9 a (spring retaining surface), which resulted duringthe aforementioned punching process. Further, each coil spring retainingportion 9 has a surface 9 d which was created by chamfering the cornerbetween the top surface 9 e and lateral surface 9 a. By the way, it isnot mandatory that all the spring retaining portions 9 are provided withthe surface 9 d (surface created by chamfering). That is, all that isnecessary is that at least one of the multiples spring retainingportions 9 is provided with the surface 9 d (created by chamfering). Thepresence of surfaces 9 d makes it easier for a user to insert the coilspring 2 into the space surrounded by the four coil spring retainingportions 9 (surfaces 9 a), since the coil spring 2 is guided by one (2c) of its lengthwise ends, with respect to the axial line of the coilspring 2 when the coil spring 2 is inserted into the space surrounded bythe four lateral surfaces 9 a of the four retaining portions 9.

Referring to FIG. 4, the coil spring 2 is formed by spirally winding apiece of wire. The lengthwise end portions of the piece of wire are bentoutward of the coil spring 2 with respect to the radius direction of thecoil spring 2, yielding thereby two bent portions 2 b and 2 f.

As the driver gear 4 is rotated in the direction indicated by the arrowmark B in FIG. 2, the friction between the aforementioned other endsurface 2 d of the coil spring 2, and the driver gear 4, acts on thecoil spring 2 in a manner to rotate the coil spring 2. However, as thecoil spring 2 begins to rotate, the bent portion 2 b comes into contactwith the one of the coil spring retaining portions 9, preventingtherefore the coil spring 2 from rotating further. Thus, it is possibleto prevent the coil spring 2 from rotating with the driver gear 4. Thatis, each of the lengthwise ends of the piece of wire of which the coilspring 2 is formed is bent to provide the coil spring 2 with the bentportion 2 b (2 f) which is protrusive beyond the periphery of the coilspring 2. Thus, as the friction between the coil spring 2 and drivergear 4 begins to rotate the coil spring 2, the bent portion 2 b comesinto contact with one of the multiple coil spring retaining portions 9,and therefore, the coil spring 2 is prevented from rotating further.

<First Step in Operation to Assembling Driving Force TransmittingDevice>

Next, referring to FIGS. 4 and 5, how to assemble the driving forcetransmitting device 1 is described. Referring to part (a) of FIG. 5,first, an assembler is to insert the coil spring 2 (in directionindicated by arrow mark C) into the space surrounded by the four coilspring retaining portions 9 (four lateral surfaces 9 a) so that one (2c) of the lengthwise end surfaces of the coil spring 2 comes intocontact with the surface 3 b of the first side plate 3. As the coilspring 2 is inserted, it is held to the first side plate 3, between thepair of retaining portions 9(H1), which are separated from each other bythe distance L (between two surfaces 9 a). Thus, this structuralarrangement can reduce the possibility that the coil spring 2 willdislodge from the space surrounded by the four retaining portions 9.That is, it improves the coil spring unit CS in the efficiency withwhich the coil spring unit CS can be assembled.

After the completion of the first step in the process of assembling thedriving force transmitting device 1, the combination of the coil spring2 and first side plate 3 is referred to as an assembly 10.

<Second Step in Operation to Assemble Driving Force Transmitting Device>

After the completion of the above-described step in the operation forassembling the driving force transmitting device 1, the assembler is toattach the assembly 10 to the driving force transmitting device 1 towhich the second side plate 6, follower gear 5, and driver gear 4, whichare shown in FIG. 2, have just been attached.

<Reason for Retaining Coil Spring 2 by Lateral Surfaces 9 a (RetainingSurfaces)>

The multiple coil spring retaining portions 9 are created by subjectingthe first side plate 3 to the punching process and bending process insuccession. Each of the multiple retaining portions 9 has a lateralsurface 9 a which is roughly perpendicular to the line, along which theprecursor of each retaining portion 9 is bent to yield the retainingportion 9. That is, the coil spring unit CS is structured so that as thecoil spring 2 is inserted into the space surrounded retaining portions9, a line which coincides with the point of contact between theperipheral portion 2 a of the coil spring 2, and the retaining portion9, and is tangential to the peripheral portion of the coil spring 2,becomes roughly parallel to the lateral surface 9 a of the retainingportion 9. Thus, the lateral surface 9 a of each of the multipleretaining portions 9 functions as a surface for retaining the coilspring 2.

Even if the multiple coil spring retaining portions 9 are different inthe angle at which they are bent in the bending process, the amount ofthe positional deviation of the lateral surface 9 a (coil springretaining surface) with respect to the radial direction of the coilspring 2 is relatively small. That is, the effect of the bending processupon the distance L1 between the mutually opposing two surfaces 9 a isrelatively small. Thus, this embodiment can improve the coil spring unitCS in the accuracy with which the coil spring 2 is attached to the firstside plate 3.

That is, the distance L1 between the mutually opposing lateral surfaces9 a is set primarily by the measurements of the metallic mold used tomake the coil spring retaining portions 9 through the punching process(effect of bending process is small). Therefore, each lateral surface 9a is highly precisely positioned relative to the main portion of thefirst side plate 3.

Because it is possible to prevent the problem that when a substantialnumber of the first side plate 3 are manufactured, they are different inthe amount of the distance L1. Therefore, it is unlikely to occur thatthe coil spring 2 dislodges from the first side plate 3, and falls,during the second step in the operation for assembling the driving forcetransmitting device 1.

<Operation to Twist Coil Spring>

By the way, it is possible to utilize the bent portion 2 b of the coilspring 2 in the first step in the operation for assembling the drivingforce transmitting device 1, as follows. First, an assembler is toinsert the coil spring 2 into the space surrounded by the four lateralsurfaces 9 a. Then, the assembler is to rotate the coil spring 2 in thedirection indicated by the arrow mark B in part (b) of FIG. 5 so thatthe bent portion 2 b of the coil spring 2 comes into contact with thesurface 9 f of one of the coil spring retaining portions 9. Then, theassembler is to rotate the coil spring 2 further in the directionindicated by the arrow mark B in part (b) of FIG. 5, that is, thedirection in which the piece of wire was wound to form the coil spring2, so that the coil spring 2 is twisted.

As the coil spring 2 is twisted, the diameter D1 of the peripheralportion 2 a of the coil spring 2 (external diameter of coil spring 2)reduces to a diameter D2, which is indicated by a broken line in part(b) of FIG. 5 (D2<D1). That is, while the coil spring 2 is remainingtwisted in the direction indicated by the arrow mark B in part (b) ofFIG. 5, the diameter D2 of the peripheral portion 2 a of the coil spring2 is sufficiently smaller than the distance D1. Thus, the assembler isto insert the coil spring 2 further into the space surrounded by thefour lateral surfaces 9 a until the one (2 c) of the lengthwise endsurfaces of the coil spring 2 in terms of the direction parallel to theaxial line of the coil spring 2 comes into contact with the surface 3 bof the first side plate 3 while keeping the coil spring 2 twisted asdescribed above.

Then, the assembler is to release the coil spring 2 while keeping theone (2 c) of the lengthwise end surfaces of the coil spring 2 in contactwith the surface 3 b of the first side plate 3. Consequently, theexternal diameter D1 of the peripheral portion 2 a of the coil spring 2is increased to the normal one D1 (>D2) by the resiliency of the coilspring 2. Thus, it is ensured that the coil spring 2 is retained betweenthe top and bottom lateral surfaces 9 a; it is remain securely held tothe first side plate 3.

Modified Version 1 of Embodiment 1

In the first embodiment described above, the coil spring unit CS wasstructured so that the coil spring 2 is held to the first side plate 3by coil spring retaining portions 9 of the first side plate 3, by beingsandwiched by its peripheral portion 2 a, by the retaining portions 9.Part (a) of FIG. 6 is a side view of the combination of the coil springretaining portions 9 of the first side plate 3, and the coil spring 2,in the first modified version of the first embodiment. In the firstmodified version of the first embodiment, which is shown in part (a) ofFIG. 6, the first side plate 3 is structured so that the lateral surface9 a of the top retaining portion 9, and the lateral surface 9 a of thebottom retaining portion, face the inward side 2 e of the coil spring 2,and the slant surface 9 d is formed by chamfering the corner between thelateral surface 9 a and top surface 9 e. That is, it is structured sothat the coil spring 2 is retained by its inward side 2 e, by the two(top and bottom) lateral surfaces 9 a, shown in part (a) of FIG. 6. Bythe way, if the coil spring 2 is displaced, not only is it retained bythe two (top and bottom) lateral surfaces 9 a, but also, the lateralsurface 9 a of one of two (left and right) coil spring remainingportions 9(H2).

Modified Version 2 of Embodiment 1

Part (b) of FIG. 6 is a side view of the combination of the coil springretaining portions 9 of the first side plate 3, and the coil spring 2,in the second modified version of the first embodiment. In the secondmodified version of the first embodiment, which is shown in part (b) ofFIG. 6, the first side plate 3 is provided with three coil springretaining portions 9, which were made through the punching process andbending process. The three retaining portions 9 are separated by 120° interms of the circumferential direction of the through hole 3 a withwhich the first side plate 3 is provided. Thus, the coil spring 2 isretained by the lateral surface 9 a of each of the three remainingportions 9, by its peripheral portion 2 a. By the way, the first sideplate 3 may be provided with four or more coil spring retaining portions9 so that the coil spring 2 is retained by its inward portion, by thelateral surface 9 a of each of the four or more retaining portions 9.

Modified Version 3 of Embodiment 1

FIG. 7 is a side view of the combination of the coil spring retainingportions 9 of the first side plate 3, and the coil spring 2, in thethird modified version of the first embodiment. In the precedingembodiments of the present invention, which were shown in FIG. 6 andpreceding drawings, the first side plate 3 were structured so that thecoil spring retaining portions 9 (H2) face the peripheral portion 2 a ofthe coil spring 2. However, the surface of the retaining portion 9(H2),which faces the peripheral portion 2 a of the coil spring 2, has only toloosely retain the coil spring 2 by the peripheral portion 2 a of thecoil spring 2. Thus, it is not required to be very precisely positioned.Therefore, the first side plate 3 may be structured so that the othersurface of the coil spring supporting portion than the lateral surface 9a, which results as the first side plate 3 is subjected to the punchingprocess, faces the peripheral portion 2 a of the coil spring 2.

Thus, in this modified version of the first embodiment, the first sideplate 3 is structured so that instead of one of the surfaces of each ofthe coil spring retaining portion 9(H2), which results as the first sideplate 3 is subjected to the punching process, a surface 9 f, which is apart of the surface 3 b of the first side plate 3, faces the peripheralportion 2 a of the coil spring 2.

The coil spring unit CS shown in FIG. 7 is structured so that the two(top and bottom) coil spring retaining portions 9(H1) sandwich the coilspring 2 in such a manner that their lateral surface 9 a contacts theperipheral portion 2 a of the coil spring 2. This is how the coil spring2 is fixed to the first side plate 3.

The distance L1 between the two lateral surfaces 9 a is determined bythe measurements of the metallic die used to make the coil springretaining portions 9 by subjecting the first side plate 3 to thepunching process. Therefore, the distance L1 between the lateralsurfaces 9 a of one of the pair of retaining portions 9, and that of theother retaining portion 9, can be highly accurately set. Thus, it doesnot occur that the coil spring 2 dislodges from the first side plate 3and falls during the operation for assembling the driving forcetransmitting device 1. That is, this modified version of the firstembodiment can also increase the efficiency with which the driving forcetransmitting device 1 is assembled.

Embodiment 2

Next, referring to FIGS. 8 and 9, the combination of the coil springsupporting portion of the first side plate, and the coil spring, in thesecond embodiment of the present invention is described about itsstructure. By the way, the portions of the first side plate and coilspring in this embodiment, which are the same in structure as thecounterparts in the first embodiment, are given the same referentialcodes as those given to the counterparts, and are not described.Further, even if a given portion of the first side plate or coil springin this embodiment is different in referential code from the counterpartin the first embodiment, it is not described as long as the former isthe same in structure as the counterpart. FIG. 8 is a perspective viewof the combination of the first side plate and coil spring in thisembodiment, prior to the attachment of the coil spring 2 to the firstside plate 12. Part (a) of FIG. 9 is a side view of the combination, asseen from the direction indicated by an arrow mark C in FIG. 8, afterthe attachment of the coil spring 2 to the first side plate 12. It showsthe structure of the assembly 10. Part (b) of FIG. 9 is a sectional viewof the assembly 10 at a plane d-d in part (a) of FIG. 9.

<Apparatus Main Assembly>

First, referring to FIGS. 2, 3 and 8, the driving force transmittingdevice 1 in this embodiment is described about its structure. Thedriving force transmitting device 1 in this embodiment is virtually thesame as that in the first embodiment, except that in this embodiment,the first side plate 12 is employed in place of the first side plate 3shown in FIGS. 2 and 3. Thus, it is not described in detail in order notto repeat the same descriptions.

<Coil Spring Retaining Portions>

Next, referring to FIG. 8, the coil spring retaining portions 9 and 11,with which the first side plate 12 is provided, are described abouttheir structure. Referring to FIG. 8, the first side plate 12 in thisembodiment is provided with three coil spring retaining portions 9 andone coil spring retaining portion 11, which were made by a piece ofmetallic plate through a punching process and a bending process. Interms of the circumferential direction of a hole 12 a, with which thefirst side plate 12 is provided, the direction in which the topretaining portion 9(H1) and bottom retaining portion 11 are bent, andthe direction in which the left and right retaining portions 9(H2) arebent, are the same. Further, the retaining portions 9 and 11 areseparated by 90 degrees in terms of the circumferential direction of thehole 12 a.

The coil spring retaining portions 9 are the same in structure as thosein the first embodiment. Thus, their structure is not described indetail in order not to repeat the same descriptions. The coil springretaining portion 11 in this embodiment has a lateral surface 11 a,which resulted when the retaining portion 11 was made through thepunching process. The first side plate 12 is structured so that the topand bottom retaining portions 9 and 11 are separated by 180 degrees interms of the circumferential direction of the hole 12 a, and also, thatthe lateral surface 9 a of the retaining portion 9(H1) and the lateralsurface 11 a of the retaining portion 11 face each other across the hole12 a. The distance between the lateral surface 9 a of the top retainingportion 9(H1) and the lateral surface 11 a of the bottom retainingportion 11 is roughly equal to the diameter D1 of the peripheral portion2 a of the coil spring 2. Thus, as the coil spring 2 is inserted betweenthe lateral surfaces 11 a and 9 a, it is retained by the retainingportions 11 and 9, by its peripheral portion 2 a.

The distance L2 between the lateral surface 9 a of one of the two (leftand right) coil spring retaining portions 9(H2), and that of the othercoil spring retaining portion 9(H2) is set to be roughly 1 mm largerthan the distance L1.

Further, the lateral surface 11 a of the coil spring retaining portion11 has such a width that is equal to the diameter of the wire of whichthe coil spring 2 is made. Further, the retaining portion 11 has anoffset surface 11 g which is protrusive beyond the lateral surface 11.Further, it is provided with a bottom surface 11 c, which roughlyvertically connects the lateral surface 11 a and offset surface 11 g.Thus, the combination of the lateral surface 11 a and bottom surface 11c makes up a coil spring hooking portion 11 b.

The coil spring hooking portion 11 b is protrusive, in the radiusdirection (upward in part (b) of FIG. 9) of the coil spring 2, to theadjacencies of one of the edges of the lateral surface 11 a (coil springretaining surface), in terms of the thickness direction of the firstside plate 12 (coil spring holding member). At least one among themultiple coil spring retaining portions is provided with the hookingportion 11 b. When the coil spring 2 is in engagement with the hookingportion 11 b, and the coil spring 2 is retained by the retainingportions 9 and 11, it is possible for the bent portion 2 b (engagingportion) to be in contact with the surface 11 f of the retaining portion11. The surface 11 f of the retaining portion 11 is a part of thesurface 12 b of the first side plate 12. The slant surface 11 d isbetween the offset surface 11 g and top surface 11 e.

<First Step in Operation to Assemble Driving Force Transmitting Device>

Next, referring to FIGS. 8 and 9, the first step in the operation toassemble the driving force transmitting device 1 is described. In thisembodiment, first, an assembler is to attach the coil spring 2, shown inFIG. 8, to the first side plate 12. Then, the assembler is to turn thecoil spring 2 in the direction indicated by an arrow mark B in part (b)of FIG. 9 until the bent portion 2 b of the coil spring 2 comes intocontact with the surface 9 f of the retaining portion 9. Then, theassembler is to twist the coil spring 2 in the direction indicated bythe arrow mark B, with the bent portion 2 b kept in contact with thesurface 9 f.

Consequently, the coil spring 2 reduces in diameter; the diameter of theperipheral portion 2 a of the coil spring 2 reduces from D1 to D2 (<D1).That is, as the coil spring 2 is twisted in the direction indicated bythe arrow mark B in part (a) of FIG. 9, the diameter of the peripheralportion 2 a of the coil spring 2 becomes smaller than the distance L3between the lateral surface 9 a of the top retaining portion 9(H1), andthe offset surface 11 g of the bottom retaining portion 11.

Then, the assembler is to insert the coil spring 2 between the lateralsurface 9 a of the top retaining portion 9(H1), and the offset surface11 g of the retaining portion 11, while keeping the coil spring 2 in thestate in which its diameter is D2.

Then, after one of the lengthwise end surfaces 2 c of the coil spring 2in terms of the direction parallel to the axial line of the coil spring2 comes into contact with the surface 12 b of the first side plate 12,the assembler is to release the coil spring (stop keeping coil spring 2twisted in direction indicated by arrow mark B in part (a) of FIG. 9).Consequently, the coil spring 2 recovers in diameter; the diameter ofthe peripheral portion 2 a of the coil spring 2 returns to D1. Thus, theperipheral portion 2 a of the coil spring 2 comes into contact with thelateral surface 9 a of the retaining portion 9(H1) and lateral surface11 a of the retaining portion 11(H1), being thereby sandwiched by thetwo surfaces 9 a and 11 a. That is, the coil spring 2 becomes securelyheld to the first side plate 12. After the fixation of the coil spring 2to the first side plate 12, the combination of the coil spring 2 andfirst side plate 12 is referred to as an assembly 13.

<Second Step in Operation to Assemble Driving Force Transmitting Device>

After the completion of the first step in the operation to assemble thedriving force transmitting device 1, the assembler is to attach theassembly 12 to the drive train assembly having the second side plate 6,follower gear 5, and driver gear 4, which are shown in FIGS. 2 and 3.Like the lateral surface 9 a, the lateral surface 11 a also is unlikelyto be affected by the bending process. That is, the bending process isunlikely to affect the distance L1. Therefore, it is unlikely for thecoil spring 2 to dislodge from the first side plate 12, and fall.

Referring to part (b) of FIG. 9, in this embodiment, the coil spring 2is anchored to the first side plate 12 by the coil spring hookingportion 11 b formed by the surface 12 b of the first side plate 12,lateral surface 11 a of the retaining portion 11, and the bottom surfaceof the retaining portion 11. Thus, even if an assembler accidentallytouches the coil spring during the operation to assemble the drivingforce transmitting device 1, it is unlikely to occur that the coilspring 2 to dislodge from the first side plate 12, and fall.

By the way, in this embodiment, the first side plate 12 was providedwith the three coil spring retaining portions 9 a and one coil springretaining portion 11. However, the embodiment is not intended to limitthe present in scope in terms of the number and positioning of the coilspring retaining portions 9 and 11. For example, the present inventionis also applicable to a driving force transmitting device having two ormore coil spring retaining portions 11 in place of multiple coil springretaining portions 9. Otherwise, the driving force transmitting device 1in this embodiment is the same in structure, as well as effect, as thatin the first embodiment. By the way, not only is the coil spring unitdescribed above applicable to an image forming apparatus such as theimage forming apparatus 110, but also, various apparatuses in variousfields.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2016-240786 filed on Dec. 13, 2016, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A coil spring unit comprising: a coil spring; anda metal plate supporting said coil spring, said metal plate including aplurality of supporting portions cooperative with each other to supportsaid coil spring, wherein said supporting portions are provided bybending said metal plate at bending lines and have supporting surfacessubstantially perpendicular to the bending lines, respectively, andwherein said supporting surfaces are substantially parallel with outsidetangential lines of said coil spring and support said coil spring.
 2. Acoil spring unit according to claim 1, wherein said supporting portionssupport said coil spring at an outer periphery of said coil spring.
 3. Acoil spring unit according to claim 1, wherein said supporting portionssupport said coil spring at an inner periphery of said coil spring.
 4. Acoil spring unit according to claim 1, wherein four such members areprovided substantially equidistantly, and a distance between two of suchsupporting surfaces which are in parallel with each other is differentfrom a distance between two of other such surfaces which are in parallelwith each other.
 5. A coil spring unit according to claim 1, wherein anend portion of wire of said coil spring is bent to project beyond anouter periphery of said coil spring, and said bent portion preventsrotation of said coil spring by abutting to one of said supportingportions.
 6. A coil spring according to claim 1, wherein at least one ofsaid supporting portions is provided with a hook portion configured toprevent disengagement of said coil spring in an axial direction of saidcoil spring.
 7. A drive force transmitting device comprising a clutchconfigured to transmit a driving force from a driving side to a drivenside, said clutch including a coil spring unit according to claim
 1. 8.An image forming apparatus for forming an image on a recording material,said apparatus comprising a rotatable member configured to form an imageon a recording material; and a drive force transmitting deviceincluding, a clutch configured to transmit a driving force from adriving side to a driven side, said clutch including a coil spring unitaccording to claim
 1. 9. A coil spring unit comprising: a coil spring;and a metal plate supporting said coil spring, said metal plateincluding a plurality of supporting portions cooperative with each otherto support said coil spring, wherein said supporting portions areprovided by bending said metal plate, and wherein each of saidsupporting portions has a surface substantially perpendicular to atangent line of an outer periphery of said coil spring, the surfacebeing provided by a flat surface portion of said metal plate before thebending.
 10. A coil spring according to claim 9, wherein an end portionof wire of said coil spring is bent to project beyond an outer peripheryof said coil spring, and said bent portion prevents rotation of saidcoil spring by abutting to one of said supporting portions.
 11. A coilspring according to claim 9, wherein at least one of said supportingportions is provided with a hook portion configured to preventdisengagement of said coil spring in an axial direction of said coilspring.
 12. A coil spring unit comprising: a coil spring; and a metalplate supporting said coil spring, said metal plate including aplurality of supporting portions cooperative with each other to supportsaid coil spring, wherein said supporting portions project from a flatsurface portion of said metal plate, and wherein said supportingportions each have a supporting surface configured to support said coilspring, and wherein each of said supporting surfaces is provided withsaid supporting surface substantially parallel with a tangent line of anouter periphery of said coil spring.
 13. A coil spring unit according toclaim 12, wherein four such members are provided substantiallyequidistantly, and a distance between two of such supporting surfaceswhich are in parallel with each other is different from a distancebetween two of other such surfaces which are in parallel with eachother.
 14. A coil spring unit according to claim 12, wherein an endportion of wire of said coil spring is bent to project beyond an outerperiphery of said coil spring, and said bent portion prevents rotationof said coil spring by abutting to one of said supporting portions. 15.A coil spring unit comprising: a coil spring; and a metal platesupporting said coil spring, said metal plate including a plurality ofsupporting portions cooperative with each other to support said coilspring, wherein said supporting portions includes portions projectedfrom a flat surface portion of said metal plate, and wherein a flatsurface portion of each of said projected portions is substantiallyperpendicular to a tangent line of an outer periphery of said coilspring.
 16. A coil spring unit according to claim 15, wherein four suchmembers are provided substantially equidistantly, and a distance betweentwo of such supporting surfaces which are in parallel with each other isdifferent from a distance between two of other such surfaces which arein parallel with each other.
 17. A coil spring unit according to claim15, wherein an end portion of wire of said coil spring is bent toproject beyond an outer periphery of said coil spring, and said bentportion prevents rotation of said coil spring by abutting to one of saidsupporting portions.